Standard Deviation: classification of a population or sample

Hi all,

So I understand the variance and Standard Deviation formulas well, my only problem is somewhat more qualitative.

Basically I struggle sometimes with when items are considered to be a sample and when they are considered to be a population. I know that a sample is a portion of the population My bigger problem is when I am given a set of occurences, I am not always sure of when they are a sample (N -1) or when they are a population (N).

For example, when a question discusses a “portfolio and the sets of returns within it” I think to myself - “a portfolio allows us to view ALL occurences, not just a portion, therefore this is a population”. but I’m just wondering if thoughts like this are ok.

Any suggestions on how to better classify between a population and a sample?